About this time of year, I receive calls from property owners about whether or not they should be pruning their trees in the fall. For sure, if you have not had your deciduous (leaf-dropping trees and shrubs) pruned for some time, you probably should. You may need to call a certified, licensed tree-pruning company to do the work. Here are some suggestions you may want to keep handy for future reference.
Dead, damaged, rubbing and stub branches should be removed on a regular basis. Always prune twigs and branches back to a junction point with another branch or stem. Never prune in the middle of a twig or branch. Prune only with sharp tools, as dull ones will do more damage to the plants. There are small files that can be used to sharpen the curved blades of hand pruners.
October is the best time to prune deciduous trees and shrubs. Late March and April are fine too, except if you are pruning maples and birches — they will bleed sap if pruned too close to spring.
Always sterilize pruning tools after every cut when pruning diseased wood. Use one part bleach to five to nine parts water, or denatured (rubbing) alcohol, or methyl hydrate. Oil your tools after use to prevent rusting. If you are uncertain that the wood you are pruning is diseased or not, sterilize the tools anyway. I follow this simple rule: prune and then sterilize. Sterilize the pruning tool after each cut to be safe.
When pruning branches over three inches in diameter, make an undercut first so that upper cuts will not tear the bark of the branch leading to the main trunk, thereby damaging the trunk. Make the second cut away from the first, further towards the end of the branch. The final cut should be made near the bark of the branch or trunk. Never cut into the branch bark ridge located in the crotch, but always on the side of the branch bark ridge closest to the branch that will be removed. The final cut should continue to the branch collar — an area of some swollen wood and bark out a very short distance from the main trunk or branch adjacent to the branch that will be removed. Never leave a short stub branch when pruning, as this will be an entry point for diseases and insects. When I examine trees for clients, I see that in the majority of trees, the client has improperly pruned the branches. So many people believe that leaving a pruning stub is best for the tree. This is simply not true.
Evergreen trees and shrubs such as spruce, pine and fir can be easily pruned to control the horizontal spread of their growth. Simply prune off the terminal bud, or terminal twig or branch.
June is the best time to prune evergreens. Never prune off more than a quarter of the living evergreen growth on cedars and junipers. Many people over-prune cedar shrubs, especially by giving them a severe "haircut." Prune back to a junction with another side bud, twig or branch. This will encourage bushiness in the evergreen. Any side bud, twig or branch can be pruned if growth is not wanted in the direction that the bud, twig or branch is pointing.
Never top an evergreen tree with a stem diameter greater than two inches. Excessively large topping cuts will encourage wood decay fungus to spread into the tree, causing adjacent branches and needles to die.
Do not use pruning paint products to cover over pruning cuts. They simply do not work and have been shown to be ineffective. The turpentine in many of these products can actually damage living wood and make the pruning cut too difficult to properly seal over. For large cuts of five or more inches in diameter, or for sections of the trunk or large branches that have been ripped away from the tree due to severe weather effects, you could carefully apply a clear wood preservative by brush or place a tree-pruning seal over the area. Do not place preservative on the edge of the bark-wood interface. The preservative will likely kill the cells under the bark.
Trees are very valuable in our home landscapes. To keep them looking their finest, knowing how to properly prune them for function and esthetics can be a deciding factor in enhancing the market value of your property. Twice a year, I do put on courses for the public on how to properly prune trees. The courses are usually organized and publicized through the Louis Riel School Division continuing education program.
Get in touch with me if you need more information about tree care.
Michael Allen M.Sc.F., RPF (ret’d) is a consulting urban forester, tree diagnostician and certified arborist. He owns Viburnum Tree Experts. He can be reached at 204-831-6503 or 204-223-7709. His website is treeexperts.mb.ca